As the demand for higher densities of magnetic data recording has increased, the areal density of recording is being limited by conventional cobalt-alloy media, which are reaching a fundamental limit due to thermal instabilities. To further increase the density, it is necessary to increase the magnetic anisotropy, to reduce the media grain size and variance, and to magnetically decouple the grains. For the grains to be thermally stable for 10 years, the ratio of KuV to kbT must be greater than 40, wherein Ku is the magnetic anisotropy constant, V is the grain volume, and KbT is the thermal energy. In order to maintain the signal-to-noise ratio, as the areal density increases, the volume of the grain must decrease. However, for smaller grains to remain thermally stable, a magnetic material with a higher Ku must be used to prevent super-paramagnetism. On the other hand, the maximum Ku that may be used with conventional read/write heads is limited, because the maximum field that can be produced by a magnetic recording head is limited by the saturation flux density of the head material. This limitation has recently caused considerable interest in bit-patterned magnetic recording (BPMR) and heat-assisted magnetic recording (HAMR), in which heat generated by a laser is used to heat the media and lower the magnetic anisotropy momentarily during the write process, making it possible to write a high anisotropy medium.
A very promising magnetic media candidate for BPMR and HAMR is L10 iron-platinum (FePt), which has a high bulk magnetocrystalline anisotropy energy constant Ku of ˜7×107 ergs/cc and is relatively corrosion resistant. At room temperature, grain sizes as small as 3 nm could, in theory, be thermally stable in FePt. If such small grains could be fabricated and written, the areal density that FePt media could support is well beyond 1 Tbit/in2.
Although high anisotropy L10 FePt thin films have attracted significant research attention for the past decade, no one has reported the ability to make well-ordered L10 FePt films with columnar grain structure and perpendicular texture (i.e., preferred crystal orientation of grains wherein the crystal axis along which the magnetic easy axis lies is perpendicular to the substrate), well-isolated grains, small grain size, and high coercivity, all of which are needed simultaneously in order to achieve HAMR at densities beyond 1 Tbit/in2.